Evidence for filamentary superconductivity nucleated at antiphase domain walls in antiferromagnetic CaFe2As2

Abstract

Resistivity, magnetization, and microscopic 75As nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe2As2 exhibit anomalous features that are consistent with the collective freezing of domain walls. Below T*≈10 K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and 75As NMR measurements reveal the presence of slow fluctuations of the hyperfine field. These features in both the charge and spin response are strongly field dependent, are fully suppressed by H*≈15 T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.